9.5A: HVAC System Recommendations

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Mar 4, 2023 8:47 PM
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I tried my best to meet the spatial design goals, making the HVAC design as unintrusive upon the space as possible — I had to reduce the heights of much of the ducting because the floor to floor height is so limited. Ultimately, I was able to maintain 8’ 6” ceilings on both levels, but with some difficulty. Using the duct sizing tool, I found that while many of the ducts downstream were rather small and non-intrusively sized, the upstream ducts began to get rather large. I kind of ‘cheated’ a little bit by increasing their fpm to 1200 or 1500 in order to keep their heights under 10 inches but also stay under the 1:3 aspect ratio we like to keep for rectangular ducts. I know this goes against Glenn’s recommendations that we use 1000 fpm as our maximum, but based on my experience in CEE 256 I feel like a little more airflow wouldn’t be that bad.

While I was really cognizant of the beam placements and atria, when routing my ducting, I wasn’t careful enough with respecting the column grid, and the clash detector found that I had run through a couple columns with my ductwork — I would need to go back and push my ducting around a little bit to avoid these.

I used the plenum return strategy on the ground floor, because there were more obstacles to placing ducting there than on the upper level (going around stairs, etc.), and using the grille at the side of the duct and a return terminal connected directly into the ceiling space alleviated some of my routing difficulties (you can see this in the isometric and plans below).

If I were to recommend some sustainability strategies, I’d say we might want to increase the number of zones above just the four. I think some of the spaces in the same zone as it stands right now might have different heating and cooling needs (i.e. offices vs meeting spaces, or open areas vs closed meeting rooms), and allowing for a greater number of temperature controls could reduce the amount of energy we waste on heating and cooling. In addition, I might recommend that we use circular ducts instead of rectangular ducts as they can handle higher airflows and can reduce the amount of ducting material we use on the project.


Initial impressions:

  • The floor to floor height in this model is rather small, at only 12 feet between floors. On the first floor (Level 0), the structural system was set 5 inches below the next level to accommodate the floor on the level above, and the structural framing I used was generally 12 inches deep. With around 1.5 ft removed, I’d have maybe 2.5 ft for the ducts if I want an 8 foot ceiling. There is slightly more space on the second floor
  • All the spaces look well defined and properly bounded; they all have some volume
  • I would probably make small changes to the number of people assumption — based on the original model, there is less than 1 person in each office; and I think a more reasonable assumption would be to have at least a full person in each office so I adjusted those air flows accordingly
  • There are 4 zones defined, upper and lower level East and West; West generally contains smaller confined spaces and East contains more open areas

This is what my space schedule looked like after placing the air terminals and making the adjustments for the office rooms:


I used the duct sizing tool to size my supply ducts and just chose a reasonable size for the return ducts based on the supply duct sizes.

Floor 0:


Floor 1: